Rhinoviruses, one of the “usual suspects” responsible for common colds, appear to boot out the SARS-CoV-2 virus from cells, theoretically offering some small level of protection from COVID-19. This is the idea behind a new study published today in the Journal of Infectious Diseases led by scientists at the MRC-University of Glasgow Centre for Virus Research in Scotland.
The team found that human rhinovirus (aka HRV, the virus that causes most common cold infections) can block the replication of SARS-CoV-2 (the virus that causes COVID-19) in cells of the respiratory tract. In other words, if you place HRV and SARS-CoV-2 in a petri dish of human bronchial cells, the coronavirus will struggle to take hold and the rhinovirus infection will rule supreme.
“This effect was observed irrespective of whether the viruses are used as simultaneous co-infections or infections were staggered, e.g. SARS-CoV-2 infection followed 24 hours later by HRV infection,” commented Professor Lawrence Young, Professor of Molecular Oncology at Warwick Medical School, who was not involved with the study.
This inhibitory effect, the study authors found, was most likely due to HRV sparking an innate immune response in human respiratory cells, known as the interferon response.
“The study also showed that this inhibitory effect was due to HRV inducing robust activation of the interferon-mediated innate immune response. The interferon response induced by SARS-CoV-2 infection is much lower and weaker,” explained Professor Young.
The team used mathematical modeling to see whether HRV infections could effectively outcompete SARS-CoV-2 infections in a simulated population. As they anticipated, the researchers found that the number of new SARS-CoV-2 infections decreased as the number of HRV infections increased, suggesting that the common cold virus may have the power to halt the spread of SARS-CoV-2 within a population.
“Virologists already know about the ‘viral interference’ between rhinoviruses and seasonal influenza [flu] – innate host immune responses (including interferon) induced by rhinoviruses can reduce the successful infection of influenza in humans. The fact that rhinoviruses may also ‘interfere’ with SARS-COV-2 infection is intriguing and needs further confirmation,” Dr Julian Tang, Honorary Associate Professor in Clinical Virologist at the University of Leicester, said.
This intriguing idea has only been tested out in the lab so far, so the findings should be treated with caution — people should not, for example, go sniffing around for a common cold in an attempt to protect themselves from COVID-19. Experts in the field say the study, although certainly interesting, has some important limitations to consider. For example, there are over 160 known strains of rhinovirus and it’s uncertain whether they would all have the same effect on SARS-CoV-2 infections.
“Translating this to the situation in real life is very tricky. Although it is likely that a common cold virus such as rhinovirus would induce a strong innate immune response that could block SARS-CoV-2 infections, it would still require both infections to occur at a similar time," noted Proffessor Gary McLean, Professor in Molecular Immunology, London Metropolitan University, who was also not involved in the study.
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